My Macs have always been stable... until I upgraded to Mavericks. Since that time, my iMac ( late 2012 model ) seems try randomly struggle either closing or opening Safari. I was hoping the latest update would fix the issue, but it didn't. The fix thus far has been a simple reboot. Today I stumbled upon a related issue. When Safari won't open or close, I have found that iCloud Preferences ( in System Prefs ) also won't open and that will hang System Prefs. Has anyone else seen this?